Jewel [1]}, [2]} simulates the QCD evolution and re-scattering of hard partons in a background medium. It builds on PYTHIA 6.4 [3]}, which is used for hard matrix elements, initial state parton shower and hadronisation. Jewel implements the final state parton shower interleaved with re-scattering and provides a simple model for the background medium. Re-scattering in the medium is described by LO matrix elements supplemented with a parton shower, such that both elastic and inelastic scattering are included with leading-log correct relative contributions. The interplay between different sources of radiation is governed by the formation time in such a way that always the emission with the shortest formation time gets realised. The coherence between several scattering processes within the formation time of the same emission giving rise to the LPM effect is included in a probabilistic formulation.
